I think there was an experiment with a cat where they actually generated an image from what fell on the cat's retina.
The only study I've ever seen on this has been based on simply grabbing the image off the reflection of the eye. I can't imagine this actually involved hooking up a cat's visual cortex to some sort of interface, the sheer processing power required for that sort of visual information processing is unfathomable.
They did do that, it was in Scientific American in an article about the eyes. They they did not take it from the visual cortex though, but rather from neurons coming from the retina.
The retina has various layers and they took a look at what each layer does.
They put smashed bananas into the cats' brains to record the signals.
(It's less ridiculous than it sounds: Bananas contain a certain enzyme that helps to capture the neurons signals. The porridge they put around the sensors in the cats' brains contained many more things besides the bananas. My fiancee was studying that stuff in university.)
The only study I've ever seen on this has been based on simply grabbing the image off the reflection of the eye. I can't imagine this actually involved hooking up a cat's visual cortex to some sort of interface, the sheer processing power required for that sort of visual information processing is unfathomable.
If not, link me!